I can’t see clearly because of the size of the photo, but I would say either “compass” or “marking gauge”.
Looks like a trammel to me. Normally used for striking long arcs.
Again because of the photo size, hard to tell but I suggest a caliper for measuring distance of the rail line from the stringer. Where did the photo come from?
I tend to agree with Honolulu that it’s some sort of caliper to measure from centerline to each rail. The pic makes it tough though. If you could see the other end it would tell a lot. Might be a trammel.
ralph.
…ambrose…
but only by
it’s close friends
Ah, again I’m reminded that I can be a little slow on the uptake. I get an email saying Ambrose replied to my post. I pot it open and wonder “what does ‘Ralph’ have to do with my post?” Is Honolulu Ralph? I’m not Ralph. I took me 5 or 10 seconds to get it. It’s the tool dummy 
Sheesh! I’m too young to be this old.
From the pic I’d guess could be used for measuring depth of concave.
Red_Boards are faster!
I don’t know.
Hey , let’s call it a ‘deanbo’.
Cheers
Mooneemick
I’ll agree on the trammel - good for those times when a compass or divider is too small. Plus ( having had a look at http://en.wikipedia.org/wiki/Trammel_points to double-check myself ) a number of other uses I hadn’t realised. Machinists like them, as well as woodworkers.
For what it’s worth, I can see a very good use for 'em in doing outline shapes, given a board to copy from right beside it. Just take your half-widths from the original and swing an arc from the centerline of the new blank.
Connect the arcs with a batten that comes tangent to 'em and there you have it.
Of course there’s a sketch. You think I’d describe a process that badly without doing a sketch to really screw everybody up?
You could also use this to make templates… and if you wanted to stretch things a little, it’d be pretty straightforward too. Or get a series of measurements without resorting to a ruler or tape measure or…
Hope that’s of use
doc…
Hmm, rather not. I got the pic off the Teccel website, link below.
Aloha Doc,
I always guessed you were an engineer from Stanford, MIT, School of Mines, or from Hard Knox, but no matter the background, I wish you had sat next to me in Mrs. Jones geometry class back in 64.
Enjoy the ride!
Richard
I right clicked image and then clicked “properties” on Teccel site…
“Regua_de_Outline_DSD.jpg”
Translation:
régua
- rule for measuring
- ruler for measuring
1. of outline
Interesting that I could not find the tool on the website.
Ok then … a trammel it is .
and you can make them out of string.
Cheers
Mooneemick
Could be a good tool for measuring the width of a board?
Uhhhmmm- I think my geometry guy was …you know, I have no idea what his name was. And as it was around '66, I kinda spent it in a vague haze of one sort or another.
But five years of Eng. School ( mechanical engineering ) does leave some traces. Though I should note that that is more from the Muldoon School of Boatbuilding. My Old Man ( known in the fishing trade around here as Muldoon ) showed me how to use a batten and a compass- or trammels - to get the shape of a replacement plank, an odd curvilinear thing that often twisted and many other delights. .
For that matter, after putting together that answer, it occurred to me that there’s a way to do and keep an outline template with no more than a single wood batten and a big compass or a trammel setup. With as many points on it as you could want. I’ve got to run ( Time and Tide wait for no man, etc ) but when I get back I’ll sketch it out.
off to the clam flats
doc…